Generally, the heat insulating property (λF) of polyurethane foam can be represented by the following equation:λF=λm+λg+λr 
in which:
λm is the adiabatic index through a polymer matrix,
λg is the adiabatic index through a gas within a closed cell of the foam, and
λr is the adiabatic index through thermal radiation.
In the above equation, the heat insulating property of the gas λg refers to the adiabatic index of a gas component of a blowing agent existing in the polyurethane foam (the closed cell) and makes up to 60˜70% of the total adiabatic index of polyurethane foam.
Chlorofluorocarbons (CFCs) are conventionally used as blowing agents in the production of foams. However, CFCs are regarded as detrimental to the environment and have a high Global Warming Potential (GWP) and a high Ozone Depletion Potential (ODP). Therefore the production and use of CFCs have recently been prohibited and CFCs are being replaced by non-halogenated blowing agents, like cyclopentane. However, when cyclopentane is used as a blowing agent, the polyurethane foam can have a low heat insulating function because cyclopentane has a higher gas adiabatic index than HCFCs (Cyclopentane: 0.012 kcal/m.h.° C. compared to HCFCs: 0.0094 kcal/m.h.° C.) and the foam can have a large closed cell size.
In the above equation, the heat insulating property of the solid (the polymer matrix) λm refers to the adiabatic index of the urethane resin comprising the rigid polyurethane foam and makes up 10˜20% of the total adiabatic index of polyurethane foam. Also in the above equation, the heat insulating property of radiation λr refers to the radiation adiabatic index of the closed cell of polyurethane foam and makes up 20˜30% of the total adiabatic index of polyurethane foam.
With regard to λg, it is difficult to enhance the heat insulating property of the gas when using cyclopentane. Yet, as discussed herein, because chlorofluorocarbons are regarded as harmful to the environment, cyclopentane has been suggested as a substitute for CFCs. Further, with regard to λm, unless the polyurethane foam per se is substituted, it can be difficult to improve its heat insulating properties. With regard to λr, this can be lowered by decreasing the size of the closed cell.
Korean Patent Application No. 2004-0034455 is directed to methods for preparing rigid urethane foam. Polyurethane cell size is regulated by adding a nucleating agent such as perfluorinated alkene to enhance the heat insulating property of the rigid polyurethane foam. Although nucleating agents can enhance heat insulating properties, nucleating agents such as chlorofluorocarbons also can be harmful to the environment.
As discussed herein, because many halogen-based hydrocarbons blowing agents can be harmful to the environment, there is a growing need for non-halogenated hydrocarbon blowing agents. However, using a non-halogenated hydrocarbon such as cyclopentane may induce fire risk and increase*costs. U.S. Pat. No. 7,230,036 and International Application PCT/US02/16620 disclose the use of thermally expandable particles encapsulating a non-halogenated blowing agent in the production of foam. The '036 patent states that the risk of fire resulting from the use of a hydrocarbon blowing agent can be controlled by using the thermally expandable particle encapsulating the hydrocarbon. However, this patent does not identify or address issues associated with improving the heat insulating property of the foam.